1. Introduction
This invention relates to the ortho-alkylation of phenols, and more particularly, to the vapor-phase orthoalkylation of phenols by reaction of a non-ortho-alkylated phenol with an alcohol in the presence of a shaped catalyst comprising magnesium oxide bonded with silica.
2. Description of the Prior Art
In commonly assigned Hamilton U.S. Patent Application Ser. No. 371,189, filed May 29, 1964, there is disclosed and claimed a method for methylating the ortho positions of phenols by the vapor phase reaction of a phenol with methanol in the presence of magnesium oxide as a catalyst at a catalyst bed temperature in a range of 475.degree. to 600.degree. C. Under the conditions described in the Hamilton application, phenol is selectivity ortho-methylated in yields in excess of 95%. Thus, the reaction offers a means for economically converting phenol to orthocresol, a useful disinfectant and wood preservative, and for converting both phenol and ortho-cresol to 2,6-xylenol, a monomer which can be polymerized to form poly-2,6-xylenol, a high performance thermoplastic material.
While the Hamilton invention provides an economic synthesis for both 2,6-xylenol and also ortho-cresol from phenol, the service life of the magnesium oxide catalyst is relatively short due to the high temperature at which the reaction is required to take place--i.e. about 75 to 100 hours service life at the typical reaction temperature of about 530.degree. C. Also, the magnesium oxide catalyst of the Hamilton application is only moderately selective with respect to methanol with methanol selectivity being in the range of about 40 to 50%. This means that more than about two moles of methanol are required for each mole of phenol entering into reaction with the methanol. In addition, use of unmodified magnesium oxide in powdered or weakly sintered form results in a rather large induction period for maximum selectivity. The term "induction period" may be defined as the period from the time of starting the reaction to the time at which the catalyst reaches and maintains maximum ortho-alkylation selectivity. Finally, the use of magnesium oxide in powdered or sintered form provides numerous processing difficulties.